Non-essential staff stayed on the rig

Spokesman, Jamie Jardine, said no-one was injured and staff were gradually being returned to the rig.

He told BBC Scotland: "The priority was to make sure that the non-essential staff were taken somewhere safe to avoid distracting those people who were dealing with the situation.

"But the situation on the rig is now stable and we are looking forward to resuming normal operations over the next 24 to 36 hours."

He said the Health and Safety Executive had been informed about the incident.

Aberdeen Coastguard spokesman, Ross Greenhill, said: "The gas came from a well that they are now trying to plug."

The incident began just after midnight on the drilling rig - which was on contract to BP.

A North Sea platform operated by BP Amoco was temporarily shut down in June by the Health and Safety Executive.

Prohibition notices were served on the North West Hutton installation after inspectors went on board the platform, 300 miles north east of Aberdeen, to investigate a gas leak.

While they were on board a second escape occurred.

The HSE said emergency response procedures left "a lot to be desired".

No-one was injured in either of the incidents.